What Peter sugested was go from BM to subwoofer, from subwoofer to BLs, as I understand your explanation you did not try that.
Only my comment, as I read and understand the thread.
Beosound 3000, BL 4000, BL 8000, BG 2404,BG 5000, BG CD50, Beocord 5000, BM 901, BM 2400, BM 4000, BV S45, BV 3702. There is nothing we cannot do, but a lot of things we don't want to do!!